Known blade-disk assemblies in turbomachines, such as gas turbines, normally have blade retainers which, due to their geometric shape, have the effect of minimizing the service life of the blade-disk assembly or even of the entire rotor. This holds true especially when the securing elements for securing the blades on the disk are exposed to high temperatures or mounted at highly stressed locations. This is because the securing elements often create a high additional load on the blades or disk. A frequent problem with sheet-metal securing means is that these loads are transmitted through edges or points and, therefore, lead to additional stress peaks in the material. When using bent wires for securing purposes, an additional problem is to predict a defined position under load. Unwanted movement or vibration of the wire cannot be ruled out.
An example of a blade-disk assembly is disclosed in DE 10 2005 003 511 A1. The blades are arranged on a radial collar of the disk, with their root portions engaging in a circumferential anchoring groove. Radial retention of the blades is accomplished by interlocking of the blades with the radial collar. Circumferential retention of the blades is accomplished by a retaining ring which is arranged on the radial collar opposite to the blades and in toothed engagement with the blades.
British Patent Specification GB 630732 A describes a blade-disk assembly, where the blades are arranged on both sides of a radially outwardly tapering radial collar. Retention of the blades is accomplished by locking wires which are inserted into receiving or insertion grooves extending the circumferential direction, a portion of the cross-sectional profile of each such locking wire lying in the radial collar and another portion lying in the blade roots. In addition, portions of the blade roots may interlockingly engage in a circumferential anchoring groove of the radial collar.
U.S. Pat. No. 3,282,561 discloses a blade-disk assembly, where the blades interlockingly engage in a circumferential anchoring groove of the disk, and adjacent blades are connected by retaining pins which extend angularly relative to the disk and are inserted into corresponding blade root bores.
German Patent Application DE 10 346 263 A1 describes a blade-disk assembly, where the blades are inserted into a radially outwardly widening circumferential groove and secured on the disk by locking wires positioned in receiving grooves, a portion of the cross-sectional profile of each such locking wire lying in the groove walls and another portion lying in the blade roots.
U.S. Pat. No. 4,255,086 discloses a blade-disk assembly, where the blades are axially inserted into a circumferential anchoring groove through an insertion groove and are then displaced in the circumferential direction. The blades are combined to form blade groups, and when at rest are pressed radially outwardly by a wire element extending over a respective one of the blade groups. The insertion groove is configured as a notch in one of the walls of the anchoring groove. Independently of the wire element, tilting-out of the blades is prevented by interlocking with the groove walls.
German Patent Application DE 10 2004 051 116 A1 describes a blade-disk assembly, where the blades interlockingly engage in a circumferential anchoring groove. Radial retention of the blades is accomplished by interlocking with the anchoring groove. Circumferential retention of the blades is provided by longitudinal pins supported in battlement-like projections of the groove walls. The two walls of the anchoring groove are laterally closed, and thus do not have an insertion groove for insertion of the blades. The blades are inserted by a tilting movement of the blades in the axial direction of the blade-disk assembly.
German Patent Documents DE 60 202 738 T2 and DE 60 116 460 T2 describe blade-disk assemblies, where the blades are inserted into a circumferential anchoring groove and retained radially by an interlock between supporting portions of the groove walls and their blade roots. To allow insertion of the blades, the supporting portions are circumferentially spaced apart by radially open cutouts. Circumferential retention of the blades is accomplished by locking systems formed of a locking member inserted into the anchoring groove and a screw extending radially into the locking body. The locking systems are positioned between two adjacent blades and clamped by the screw between the groove base and portions of the blade platforms, with the screws pressing or bearing against the groove base. A similar blade-disk-assembly is disclosed in EP 1 801 355 A1.
French Patent Application FR 2965008 A1 describes another blade-disk assembly. In this blade-disk assembly, for example for securing the blades by means of screws, a U-shaped insert is plastically deformed between a locking member inserted in an anchoring groove and the groove base.
It is an object of the present invention to provide a blade-disk assembly which includes an alternative blade retention system and is easy to assemble and disassemble. Further objects of the present invention are to provide a method for assembling such a blade-disk assembly, and to provide a turbomachine.
These objects are achieved by a blade-disk assembly having the features of claim 1, a method having the features of claim 12, and a turbomachine having the features of claim 14.
An inventive blade-disk assembly of a turbomachine has a plurality of adjacent rotor blades and a closure blade which are inserted with root portions in a circumferential anchoring groove of a rotor disk and cooperate with supporting portions of a forward wall and an aft wall in radially interlocking relationship therewith. Moreover, the blade-disk assembly according to the present invention has at least one circumferential retention element which interlockingly cooperates with at least one of the blades, as well as a plurality of tilt-out prevention elements which are disposed between the groove base and the root portions and which, in the rest state, space the blades from the groove base when in the upper position.
The term “upper position” means that the blades are located on an upper portion of the blade-disk assembly. When the turbomachine is oriented horizontally, this is the portion above the horizontal plane. When the turbomachine is at rest, raising the blades in the upper position causes their root portions to be positioned close to the supporting portions, thereby preventing tilting-out from the anchoring groove in the rest state. In the lower position; i.e., when positioned in a lower portion of the blade-disk assembly, the blades at rest are automatically brought into contact with the supporting portions by gravity and bear thereagainst, whereby they are protected from tilting out. During operation of the turbomachine, the blades are pressed against the supporting portions by the centrifugal force acting on them, and are thereby also protected from tilting out. During operation, the tilt-out prevention elements and, due to the high centrifugal forces also the circumferential retention elements, do not perform any primary securing function. The securing function is provided solely by the supporting portions of the groove walls. This allows the rotor blades and the closure blade to assume an optimal operation position. Since the blades are tilted into place, the supporting portions can be free of blade-insertion cutouts. Preferably, the blades are tilted into place in the axial direction; i.e., about their transverse axis.
The present invention enables the blades of a blade-disk assembly to be secured axially and circumferentially by interlocking and frictional engagement. Due to the specific structural design, life-minimizing properties of the disk geometry are significantly reduced. At the same time, the specific structural design makes it possible to use low-cost securing elements, some of which may be reused after maintenance. The advantage of the blade-disk assembly of the present invention resides particularly in the omission of life-limiting insertion grooves for the blades and securing elements, and in the use of lightly-loaded securing elements. During operation, the securing elements are in contact over a large area with the adjacent components. Because of this, hardly any loads occur at points or edges, and thus no stress peaks occur in the material. The specific design enables the blades to be mounted and removed, as well as secured and end-secured, in an easy, rapid and reproducible manner, because the securing elements do not need to be plastically deformed, or need to be plastically deformed only slightly.
In one exemplary embodiment, the at least one circumferential retention element is an elongated body whose ends are inserted into two mutually aligned receiving recesses of the walls, the at least one blade having an axial recess for receiving the circumferential retention element. The receiving recesses are easy to form and, when positioned in the supporting portions, avoid weakening of the groove walls. In addition, when the receiving recesses are configured as radially open slots, the at least one circumferential retention element can be inserted in a direction from radially outward to radially inward. They may have such widths or radii that the at least one circumferential retention element is not radially inserted, but may be screwed in. Then, the rotation is preferably in a radial direction.
In an alternative exemplary embodiment, the at least one circumferential retention element is a portion of one wall, and the at least one blade has a corresponding axial setback in the platform to cooperate with the wall portion. Thus, the at least one circumferential retention element is formed as an integral portion of the disk, which further simplifies mounting and reduces the time required therefor by eliminating assembly steps.
The tilt-out prevention elements are preferably formed sheet-metal members supported with their supporting flanges or legs on the groove base. Such sheet-metal members can be produced and adapted in a simple manner and are, in particular, U-shaped or M-shaped metal sections. The shape of the sections is dependent on the blade roots, and in particular on the undersides thereof, by which the blades rest on the sheet-metal members when at rest.
In order to circumferentially retain the tilt-out prevention elements, at least some blades may have an abutment portion with which a respective tilt-out prevention element is in lateral contact.
Preferably, the blade-disk assembly has a locking element, a portion of which is located between the groove base and the root portions and which, in the rest state, spaces the closure blade from the groove base when in the upper position. Thus, the closure blade is retained in the anchoring groove in virtually the same manner as the other blades.
In one exemplary embodiment, the locking element is supported in a bore of the closure blade and enters between two adjacent tilt-out prevention elements. Since the bore is formed in the closure blade, no additional locking members are needed. Preferably, the bore is oriented radially in such a way that it extends with its longitudinal axis past the airfoil. Thus, the locking element is freely accessible.
Preferably, the locking element is a threaded element provided with an anti-rotation feature. The threaded element enables precise adjustment and eliminates the need for, in particular, plastic deformation. In addition, the threaded element allows for non-destructive removal, and is thus reusable. The anti-rotation feature prevents unintentional rotation of the threaded element.
In order to prevent loosening of the screw from the closure blade during operation, even in the improbable case that the anti-rotation feature should fail, the locking element may have a head which is thicker than its shank supported in the bore and which is disposed between two tilt-out prevention elements.
In an alternative exemplary embodiment, the locking element has a main body which is similar to a tilt-out prevention element and has a plastically deformable tab that engages in a cutout of the closure blade. The tab allows for simple and effective locking. The closure blade merely has to be formed with a cutout in its root. There is no need to form a bore, in particular an internally threaded bore, through the closure blade.
The installation of this locking element is facilitated if the main body has a plurality of tool receptacles arranged adjacent one another in the circumferential direction of the blade-disk assembly. This allows the tab of the locking element and the cutout of the closure blade to be accurately aligned with one another.
In a method according to the present invention for assembling a blade-disk assembly according to the present invention, first, a rotor disk having a circumferential anchoring groove is provided, the anchoring groove being bounded by two walls having two supporting portions located opposite each other. Then, the rotor blades are tilted into the anchoring groove, with their root portions entering under the supporting portions, and an initially inserted blade being interlockingly engaged with a circumferential retention element. Subsequently, the rotor blades are raised or spaced from the groove base, either individually or in groups, by sliding tilt-out prevention elements under their root portions. Finally, a closure blade is tilted into the anchoring groove, and preferably a locking element cooperating with the closure blade is activated. The method enables the blades to be mounted and removed, as well as secured and end-secured, in an easy, rapid and reproducible manner.
Preferably, the locking element is a threaded element and is screwed in to a depth such that it is spaced from the groove base when the rotor blades are in contact with the supporting portions. This prevents relative movements between the locking element and the groove base during operation, thereby preventing negative phenomena, such as abrasion of material or fretting between the locking element and the groove base.
A turbomachine according to the present invention, such as a gas turbine and, in particular, an aircraft engine, has at least one blade-disk assembly. The blade-disk assembly may be disposed in the compressor and/or turbine. Such a turbomachine features a heavy-duty rotor.
Other advantageous exemplary embodiments of the present invention are the subject matter of further dependent claims.